Heat-to-power conversion method and apparatus

ABSTRACT

A fluorocarbon compound possessing a low-specific heat and a low-latent heat of vaporization is forced in the liquid state through a heat exchanger and heated to within 50* F. of, but not exceeding its critical temperature, while being maintained at a pressure exceeding its vapor pressure, to produce a liquid containing vaporous nuclei which is then injected through a nozzle or other pressure-reducing device tangentially into an expansion chamber, which chamber is at a pressure below the liquids&#39;&#39; vapor pressure, whereby a portion of the liquid evaporates and separates from the remaining liquid. The vapor fraction is withdrawn from the chamber to drive a vapor engine, the engine&#39;&#39;s exhaust vapor is condensed to a liquid which is then raised in pressure and mixed with the liquid fraction from the separation chamber and recirculated through the heat exchanger.

United States Patent [451 Jan. 25, 1972 Minto HEAT-TO-POWER CONVERSION METHOD AND APPARATUS lnventor: Wallace L. Minto, Sarasota, Fla.

Assignee: Kinetics Corporation, Sarasota, Fla.

Filed: Sept. 10, 1969 Appl. No.: 856,729

U.S. Cl ..60/36, 55/459 Int. Cl.... .F0lk 25/04 Field of Search ..60/36, 92, 108; 55/459 References Cited UNITED STATES PATENTS Feldman et al. ..60/l08 Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager AttorneyStanley Wolder [57] ABSTRACT A fluorocarbon compound possessing a low-specific heat and a low-latent heat of vaporization is forced in the liquid state through a heat exchanger and heated to within 50 F. of, but

not exceeding its critical temperature, while being maintained at a pressure exceeding its vapor pressure, to produce a liquid containing vaporous nuclei which is then injected through a nozzle or other pressure-reducing device tangentially into an expansion chamber, which chamber is at a pressure below the liquids vapor pressure, whereby a portion of the liquid evaporates and separates from the remaining liquid. The vapor fraction is withdrawn from the chamber to drive a vapor engine, the engine's exhaust vapor is condensed to a liquid which is then raised in pressure and mixed with the liquid fraction from the separation chamber and recirculated through the heat exchanger.

9 Claims, 2 Drawing Figures PATENTED Jms 1972 X'IIIIHUI M ATTORNEY HEAT-TO-POWER CONVERSION METHOD AND APPARATUS BACKGROUND OF THE INVENTION The present invention is directed generally to improvements relating to the thermodynamic cycle and it relates particularly to an improved method and apparatus for converting heat into motive power.

The use of steam as a drive medium or working fluid in vapor driven engines possesses important drawbacks and disadvantages. Among these disadvantages are susceptibility to freezing, the high weight-to-power ratios and the low maximum achievable efficiency, the latter being due to the high heat of vaporization of the water and the consequent high energy losses in the condenser.

The use of other working fluids in place of steam as the drive medium overcomes many of the drawbacks accompanying the use of steam. Many of the fluorinated carbon compounds, particularly the fluorinated chlorinated compounds such as trichloromonofluoromethane (R-l l) and other of the fluorocarbons possess highly desirable properties and characteristics as drive fluids. They have low heats of vaporization so the condenser energy losses are low and their pressure-enthalpy characteristics are highly desirable.

However, the use of these fluorinated carbon compounds is accompanied by important practical drawbacks when employed in the conventional cycles. These compounds are subject to decomposition upon being heated to excessive temperatures, have small enthalpies, and under conventional conditions possess low heat transfer properties. Consequently under conventional conditions accompanying the heating and vaporization of these fluorinated compounds attendant to their use as working fluids, localized heating or hot spots occur which promote and accelerate their decomposition. Moreover, the size of the boilers and heat exchange units are large relative to their heat transfer capacity when employed with the fluorinated compounds, and the conventional heating and vaporizing procedures and apparatus otherwise leave much to be desired.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide an improved method and apparatus for the conversion of heat into motive power.

Another object of the present invention is to provide an improved method and apparatus for producing a high-pressure vapor.

Still another object of the present invention is to provide an improve method and apparatus for the production of highpressure vapors of condensable fluorinated compounds in which any heat decomposition of these compounds is eliminated.

A further object of the present invention is to provide an improved method and apparatus of the above nature characterized by their efficiency, reliability and versatility and the compactness, ruggedness and adaptability of the apparatus.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawing which illustrates a preferred embodiment thereof.

In a sense the present invention contemplates the provision of a method and apparatus for the production of a pressurized vapor from a liquid which vapor is employed as the drive medium in a vapor engine wherein the liquid is pumped through a heat exchange unit and is there heated to a temperature below its critical temperature at a pressure above its corresponding vapor pressure so that the liquid phase is maintained in the heat exchange unit, the heated liquid being discharged into an expansion chamber at a pressure below its corresponding vapor pressure to vaporize a fraction of the injected heated liquid. The vapor and liquid fractions are separated in the chamber, the liquid fraction being returned to the heat exchange unit and the vapor fraction being used to drive a vapor engine, the expanded vapor output of which is condensed and the condensate returned to the heat exchanger.

Advantageously, the working fluid is a low boiling point fluorocarbon compound having a low heat of vaporization, preferably a boiling point at atmospheric pressure of 0 F., to 250 F., and a heat of vaporization of 20 to 300 B.t.u. per pound at atmospheric pressure. Examples of highly suitable liquids are trichloromonofluoromethane (R-l l trichlorotrifluoroethane (R-l 13), R-l l4) C Cl F (R-l l5) CClF CF (R-2l6) C Cl F perfluoro cyclic ethers and amines, and (R21)CHCl F.

The temperature and pressure of the liquid in the heat exchange unit is advantageously such that the liquid is in a nucleated state, that is, the pressure and temperature is such that a portion of the fluid is present in the form of minute vaporous nuclei but is characterized by the absence of any formation of bubbles of significant dimensions. The heat transfer rate to a liquid is found to be highest when it is in such a state of nucleated boiling, however, the rate of heat transfer from the wall to the fluid drops sharply if conditions are such that bubble formation occurs, and furthermore, there is a great danger of boiler tube burnout in the event that heat transfer from the tube wall to the heated fluid drops and the tube is not adequately cooled thereby. Moreover, the above conditions are highly conducive to the local overheating of the fluid with the resulting decomposition thereof. The system described herein obviates these difficulties and improves the efficiency of heat transfer, thereby substantially reducing the physical size of the vaporizer.

The heat exchange unit conduits are advantageously of such design and dimensions and the flow rate of the liquid therethrough are such as to produce turbulent flow in the heat exchange conduits. In addition, the surface-to-volume ratio of the heat exchange conduits should be such as to effect a temperature gradient between the external heating fluid or hot gasses and the conduit wall far greater than between the conduit wall and the heated liquid.

Advantageously, the expansion chamber separating receiver is of cylindrical shape with a depending conical bottom wall, the heated liquid being injected into the chamber through a tangential nozzle to form a vortex in the chamber, the vapor fraction being obtained through a coaxial nozzle conduit in the top of the chamber and the liquid fraction being drawn from the bottom of the chamber.

In order to increase the entrance velocity and produce a pressure differential, the minimum cross-sectional area of the tangential nozzle leading into the cylindrical expansion chamber is advantageously less than, and preferably less than half of, that of the conduit leading from the heat exchanger to the nozzle. The diameter of the expansion chamber is advantageously three to 10 times that of the conduit leading to the nozzle and the height of the chamber is advantageously four to 12 times the conduit diameter, and the height of the depending conical section is preferably between two and flve times the conduit diameter. The chamber coaxial vapor outlet conduit projects into the chamber a distance of one to four times and is of a diameter of one to four times the diameter of the conduit leading to the nozzle.

The vortex produced in the chamber causes a rapid separation of the liquid and gaseous fractions with minimal entrainment each of the other. Further, centrifugal action produces a pressure gradient across the radius of the vessel so that any small droplets of liquid entrained in the gas tend to evaporate.

The subject method and apparatus produces a pressurized vapor from a low boiling point fluorocarbon in a highly efficient and reliable manner with the obviation of any decomposition or deterioration of the fluorocarbon, and the apparatus is compact, simple and rugged.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram of a heat to motive power conversion system embodying the present invention; and

FIG. 2 is a front elevational view, partially in section, of the fluid expansion and separation section thereof.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawing which illustrates preferred embodiment to the present invention, the reference numeral generally designates the improved heat to motive power conversion system which includes a heating unit 11, a vapor separator 12, a vapor engine 13, a condenser 14, a feed pump 15, and av burner 16 In typical operation the low boiling fluid and would be circulated by pump 17 through the heat exchanger 18 which typically would be comprised of a multiplicity of coiled pipes constructed of a material that is heat and corrosion resistant. The heated fluid would then pass through a pressure reducing valve 19, which is optional, and thence through nozzle 20 into the vapor separator unit 12. The liquid portion of the heated fluid would then return via conduit 21 and reservoir 22 to the pump 17 for recirculation, whereas, the vapor portion of the heated fluid would exit separator via conduit 23, pass to the engine 13 through throttle valve 24 which controls the engine 13. Exhaust from engine 13 would pass via conduit 25 into an injector 26. Within theinjector 26 the exhaust vapor from the engine is mixed with sprayed liquid from the condenser 14. The liquid from condenser 14 goes via conduit 27 to pump and thence from pump 15 via conduit 28 back to the injector 26. lnjector 26 mixes the liquid with the exhaust vapor from the engine thereby raising the pressure in condenserl4 and providing-a much greater surface for the vapor to condense upon, as well as a higher pressure within the condenser, thereby making heat transfer much more efiicient. A portion of the liquid from pump 15 travels via check valve 29 back into the heat exchanger vapor separation system ll, 12. Fuel supplied to the burner 16 is controlled via valve 32 which, in turn, is actuated by network 33 of known construction. Network 33 is controlled in turn by the sensor 30, which is responsive to the temperature of the heated fluid within the heat exchanger coils and also to the sensor 31, which is responsive to the vapor pressure inside the vapor separator 12. Temperature sensor 30 is preset to turn down the fuel supply or turn it off entirely if the temperature exceeds a preset value below the critical temperature of the working fluid. Pressure sensor 31 is arranged so as to reduce or cut off the fuel supply via network 33 if the pressure exceeds the preset value.

The expansion chamber and vapor liquid separator 12 includes a vertical cylindrical wall 40 provided with a depending conical bottom wall 41 which terminates in the dependent coaxial conduit 21. The top of chamber 12 is closed by a wall 42 through which inlet conduit projects to a point below top wall 42. A preferably rectangular inlet nozzle 34 communicates with the upper part of chamber 12 through cylindrical wall 40 in a direction tangential to the cylindrical wall 40. The nozzle 34 is preferably of greater height than width and upon the flow of liquid therethrough into chamber 12 a rotating liquid and vapor vortex is produced.

The system 10 is charged with a low boiling point fluorocarbon compound for example, trichloromonofluoromethane (Rl 1). Under nonnal operating conditions with R-l l, pressure regulator sensor 31 is adjusted to 500 pounds per square inch, absolute, fuel control network 33 adjusted for a liquid outlet temperature in pipe 18 of 380 F.

Under normal operating conditions the pressures and temperature are as above set forth. The conditions of the working liquid in pipe 18 are such that it is in a state of nucleated boiling with a highly efficient heat transfer from the pipe to the liquid. The hot pressurized liquid issues from nozzle 20 into chamber 12 in a tangentiaf direction to establish a vortex, the drop in pressure in the nozzle 20 effecting the vaporization of about 10-20 percent by weight of the liquid discharged therein under the above conditions. By reason of the strong centrifugal force accompanying the vortex the liquid fraction and vapor fractions rapidly and efficiently separate, the liquid fraction traveling to the wall 40 and flowing downwardly through funnel 41 and conduit 21 and the vapor fraction flowing upwardly through conduit 23. The vapor flows through and drives engine 12 the exhaust of which is liquified in the pressurized condenser 14 and recirculated through heat exchange unit 18 by pump 15. The liquid fraction, on the other hand, flows into tank 22 from which it is withdrawn by pump 17 and recirculated through heat exchange unit 18.

A drop in demand of pressurized vapor such as accompanies the closing down of throttle valve 24 results in an increase in the pressure in chamber 12 which in turn reduces the delivery rate or fuel to the burner 16 to return the pressure therein to the regulated value. Any tendency for the temperature in pipe 18 to drift from the preset temperature is overcome by the regulating system including network 33 and sensing element 30 which automatically varies the fuel control valve.

According to a specific example of the improved apparatus the diameter of vapor discharge conduit 23 is l.5 inches and of liquid discharge conduit 21 is 1.5 inches, the conduit 23 projecting 3 inches into chamber 12. The diameter of chamber 12 is 5 inches and its height is 8 inches and the height of conical wall 41 is 4 inches. The nozzle transverse cross section is 1 inch high and V4 inches wide and the inside diameters of pipes 18 and 20 are 1 inch each. The engine 12 is a fivecylinder reciprocating piston engine of a total displacement of 150 cubic inches and is capable of delivery with the present system about shaft horsepower.

Examples of other working fluids which may be employed and their preferred operating parameters are as follows:

The working fluid is advantageously a nonflammable compound having, at atmospheric pressure, a boiling point of 0 to 250 F., and heat of vaporization at room temperature of 20 to 300 B.t.u. per pound. It should preferably have a critical temperature of 200 to 600 F., and a critical pressure of 400 to 1,000 pounds per square inch absolute. The temperature to which the liquid is heated in heat exchanger 18 should be within 40 F., of the critical temperature and the pressure should exceed the saturation pressure by about l0 to I00 pounds per square inch. The pressure in the expansion chamber should be between 10 and 200 pounds per square inch less than the critical pressure.

While there have been described and illustrated preferred embodiments of the present invention it is apparent that numerous alterations, omissions, and additions may be made without departing from the spirit thereof.

lclaim:

l. The method of converting heat into motive power comprising the steps of heating a vaporizable liquid to a temperature not exceeding its critical temperature at a pressure not less than the vapor pressure of said liquid at the temperature thereof, reducing the pressure of said heated liquid to evaporate a fraction thereof while leaving the remaining fraction in a liquid state, separating said liquid and vapor fractions, returning said liquid fraction to said heating step, feeding said vapor fraction to a vapor engine, condensing the vapor output of said engine and returning said condensate to said heating step.

2. The method of claim 1 wherein said liquid has a critical temperature of 200 to 600 F., a boiling point at atmospheric pressure of 0 to 250 F., and a heat of vaporization at room temperature of 20 to 300 B.t.u. per pound.

thereof.

8. The method of claim 2 wherein said heated liquid is expanded to a pressure between 10 and 200 pounds per square inch less than that of said pressurized heated liquid.

9. The method of claim 1 wherein said heated liquid is projected tangentially into an expansion chamber to reduce the pressure thereof and produce a vortex enhancing the separation of the liquid and vapor fractions. 

2. The method of claim 1 wherein said liquid has a critical temperature of 200* to 600* F., a boiling point at atmospheric pressure of 0* to 250* F. and a heat of vaporization at room temperature of 20 to 300 B.t.u. per pound.
 3. The method of claim 2 wherein said liquid has a critical pressure of 400 to 1,000 pounds per square inch absolute.
 4. The method of claim 2 wherein said liquid is a fluorocarbon compound.
 5. The method of claim 2 wherein said liquid is heated to its nucleating temperature.
 6. The method of claim 2 wherein said liquid is heated to a temperature of within 40* F. of its critical temperature.
 7. The method of claim 2 wherein the pressure of said liquid during the heating thereof exceeds the critical pressure thereof.
 8. The method of claim 2 wherein said heated liquid is expanded to a pressure between 10 and 200 pounds per square inch less than that of said pressurized heated liquid.
 9. The method of claim 1 wherein said heated liquid is projected tangentially into an expansion chamber to reduce the pressure thereof and produce a vortex enhancing the separation of the liquid and vapor fractions. 